Spray a 13-by-9-inch baking pan with cooking spray, then line the pan with a 16-by-13-inch piece of parchment paper, leaving a few inches of overhang on each side. Set aside.

Combine sugar, corn syrup, and water in a small saucepan fitted with a candy thermometer and place over medium-high heat. Stir mixture until sugar completely dissolves. Place egg white in the base of a stand mixer fitted with the whisk attachment. Spray a rubber spatula with cooking spray and set aside.

Once sugar mixture is at 270°F, add salt to egg white and beat at high speed to stiff peaks, about 2 minutes.

Once sugar mixture reaches 275°F, remove from heat. Keeping the mixer on high speed, very slowly pour 1 tablespoon of the hot syrup in a thin stream down the side of the bowl (avoiding the whisk) and let it completely incorporate before adding more. Repeat until you’ve added all the syrup; it should take about 2 minutes. Continue to mix until nougat pulls away from the sides of the bowl, about 1 minute more. Turn off the mixer and, using the oiled spatula, stir in peanut butter; mixture should be thick and spongy.

Immediately turn nougat into the prepared pan and, using the oiled spatula or your hands, spread mixture evenly. Let sit uncovered while you make the caramel, at least 5 minutes.

For the caramel:

Combine all ingredients except peanuts and vanilla extract in a heavy-bottomed 4-quart saucepan fitted with a candy thermometer and place over medium-high heat. Stir mixture until sugar completely dissolves, about 2 minutes. Wash down the inside of the pan with a wet pastry brush to prevent crystallization. Boil mixture, swirling pan occasionally (but not stirring), until syrup is at 248°F, about 8 minutes.

Immediately remove the saucepan from heat, stir in peanuts and vanilla extract, and mix until peanuts are evenly distributed. Pour caramel mixture over nougat and, using an oiled rubber spatula, spread evenly in the pan. Let cool until caramel is no longer warm to the touch and is opaque, about 70 minutes. Remove nougat-caramel mixture from the pan, transfer to a parchment-lined baking sheet, and place in the refrigerator until caramel is cool and gives slightly when pressed.

Remove nougat-caramel mixture from the refrigerator and place on a cutting board, caramel side down. Cut into 4-by-1-inch rectangles (you need at least 24). Return to the parchment-lined baking sheet and place in the refrigerator to harden while you temper the chocolate, at least 20 minutes.

For the chocolate coating:

To temper chocolate, fill a large bowl with 2 inches of cold water, add 3 to 4 ice cubes, and set aside.

Bring a saucepan filled with 1 to 2 inches of water to a simmer over high heat; once simmering, turn off heat. Place 1 1/2 pounds of the chocolate in a dry heatproof bowl. Set the bowl over the saucepan and stir until chocolate is completely melted and reaches 118°F. (Make sure chocolate does not come in contact with water or exceed 120°F. If either happens, start over, as the chocolate is no longer usable.)

Remove the bowl from the saucepan. Add remaining 1/2 pound chocolate and stir until all chocolate is melted and cools to 80°F. To speed the cooling process, after all chocolate has melted place the bowl over the reserved cold-water bath.

Return the bowl to the saucepan and stir until chocolate reaches 86°F; immediately remove from heat. Do not remove the thermometer from the bowl; check the temperature periodically to make sure it stays between 85°F and 87°F. (Chocolate must remain in this temperature range while dipping or it will not set up properly.) Keep the saucepan over low heat and use it to reheat chocolate as necessary.

To test if chocolate is properly tempered, spread a thin layer on parchment paper and place it in the refrigerator for 3 minutes to set. If chocolate hardens smooth and without streaks, it is properly tempered. (If it is not properly tempered, you need to repeat the process.)

Line a baking sheet with parchment paper. Remove undipped candy bars from the refrigerator and drop them one at a time, nougat side down, into tempered chocolate. Cover caramel side with more chocolate, then remove candy bar. To do so, use a poultry lifter or hold two dinner forks in one hand, crossing the ends of the handles to form a V, with the tines pointed outward. As you remove each candy bar, tap the fork(s) several times against the edge of the bowl and scrape the bottom of the fork(s) across the edge to wipe away any excess chocolate.

Place Snickles on the baking sheet by tilting the fork(s) so the edge of each candy bar touches the parchment-lined pan, then smoothly pull the fork(s) out. Repeat until all candy bars have been dipped. Let sit at room temperature until completely set, at least 20 minutes.

Trim any excess chocolate from edges of candy bars and place Snickles in an airtight container. Snickles will last up to three weeks in the refrigerator or up to two months in the freezer. Let come to room temperature before serving